The invention relates to a shroud segment to be arranged on a blade, in particular a gas turbine blade. The invention further relates to a blade, in particular a gas turbine blade, for a turbomachine.
This type of shroud segment as well as a blade with this type of shroud segment are already known from the prior art. The shroud segment, which is arranged on a radial end area of the blade, is fundamentally used to dampen blade vibrations and is used in particular in the case of gas turbine blades for rear turbine blades. In addition, the shroud segment reduces the flow around blade tips and hereby increases the efficiency of an associated turbomachine. The shroud segments of adjacent blades of a rotor form a continuous shroud in this case. To reduce stress concentrations, known shroud segments feature a stiffening structure that is raised relative to a shroud segment surface, which is usually formed as a so-called “dog bone” or “half dog bone”.
The fact that known shroud segments must be designed to be comparatively voluminous in order to make an adequate reduction in stress concentrations possible must be considered to be disadvantageous in this case. This in turn substantially increases the overall weight of the shroud segment as well as a blade provided therewith. This also leads to high masses being moved when the blade is in operation.
The object of the present invention is to create a shroud segment as well as a blade provided with such a shroud segment, which makes a weight reduction possible with simultaneously good reduction in stress.
Advantageous embodiments with expedient further developments of the invention are disclosed in the respective subordinate claims, wherein advantageous embodiments of the shroud segment are to be viewed as advantageous embodiments of the blade and vice versa.
In the case of a shroud segment according to the invention which makes a weight reduction possible with simultaneously good reduction in stress, the stiffening structure is cross-shaped at least in some areas. Because of the cross-shaped design the stress concentrations are able to be reduced significantly in the shroud segment and the stiffness of the shroud segment is improved while simultaneously optimizing weight.
An advantageous embodiment of the invention provides that the stiffening structure comprises at least two ribs arranged in a cross-shaped manner, whose principal axes are at a predetermined angle to one another. This makes a simple and targeted adjustment of the stress level within the shroud segment possible, wherein different shroud segment types may be taken into consideration individually. In this case, it may be provided for example that the respective angle be determined as a function of the respective shroud segment geometry, the shroud segment material and the subsequent use conditions in an associated turbomachine.
In another embodiment, it has been shown to be advantageous if the principal axes of the ribs are at an angle of between 20° and 90° to one another. An especially advantageous stress distribution is hereby ensured within the shroud segment with simultaneously high stiffness.
Additional advantages are produced in that the stiffening structure comprises at least one rib, which is arranged along and/or perpendicular to a stress line of the shroud segment. Because of the stiffness that is hereby obtained in the shroud segment, an especially low stress level is achieved within the shroud segment.
Another embodiment of the invention provides that the stiffening structure comprises at least one rib, which has a constant or location-dependent height over its longitudinal extension in the profile. In other words, it is provided that one or more ribs of the stiffening structure has a uniform and/or a varying height profile over its longitudinal extension, which results in an especially precise adaptability of the stiffening structure to the respective design of the shroud segment and the individual progression of the stress lines within the shroud segment.
An optimum adaptability of the shroud segment with respect to minimum weight with a maximum reduction in stress is made possible in another advantageous embodiment of the invention in that the at least one rib has a height between 0.1 cm and 10 cm.
In this case, it has furthermore been shown to be advantageous if the stiffening structure comprises at least one rib, which has a cross-sectional profile over its longitudinal extension is selected as a function of a stress profile of the shroud segment without this rib. In other words, the cross-sectional profile of the at least one rib is formed over its longitudinal extension while taking a stress profile into consideration which the shroud segment would have without this rib. For example, the at least one rib may have a thickened cross-sectional profile in regions of potentially high stress. Conversely, a correspondingly reduced cross-sectional profile may be provided in regions with potentially low stress. As a result, a maximum reduction in stress can be produced with minimal additional weight of the shroud segment.
An increase in the shroud segment's fatigue strength is made possible in another embodiment in that the stiffening structure comprises rounded surface transitions to the shroud segment surface, because this permits the occurrence of peaks in force on the edges of the stiffening structure to be reliably prevented for example in the case of tensile or bending loads of the shroud segment.
An especially high level of stiffness of the shroud segment with optimized weight is achieved in another embodiment in that the stiffening structure laterally delimits at least one discrete shroud segment surface region. In other words the shroud segment has a depression, which is formed by the raised stiffening structure.
An especially uniform distribution of force and stress over the shroud segment is achieved in another embodiment in that the stiffening structure laterally delimits four and/or six discrete shroud segment surface regions.
Another advantageous embodiment of the invention provides that the shroud segment has two opposing contact surfaces that are essentially Z-shaped in the longitudinal section for application to corresponding contact surfaces of two other shroud segments. As a result, adjacent blades, each of which are provided with such a shroud segment, are supported on each other in pairs during the operation of an associated turbomachine or a rotor provided with these blades, thereby making an especially mechanically stable shroud possible. Undesired bending or twisting of the blades is likewise minimized through this.
An especially high level of stiffness is achieved in a further embodiment in that the stiffening structure comprises at least one rib, which extends between the two contact surfaces. As a result, it is possible to provide that the rib extends between corresponding corner regions of the two Z-shaped contact surfaces, because generally great stress concentrations may occur at these corners.
A further aspect of the invention relates to a blade, in particular a gas turbine blade, for a turbomachine, comprising a shroud segment arranged on a radial end area of the blade, which has a stiffening structure that is raised relative to a shroud segment surface. A reduction in the weight of the blade with simultaneously good reduction in stress is achieved according to the invention in that the stiffening structure is cross-shaped at least in some areas. Because of the cross-shaped design, the stress concentration in the shroud segment may be reduced significantly and the stiffness of the shroud segment is improved with simultaneous weight optimization.
It has been shown to be advantageous in this case if the shroud segment is designed according to one of the preceding exemplary embodiments. The advantages that are produced in the process can be found in the corresponding descriptions.
An especially high level of mechanical stability and loading capacity of the blade is achieved in another embodiment in that the shroud segment is designed to be one piece with the blade. Although the shroud segment and the blade may fundamentally also be designed to be two-piece or multi-piece and may be joined in a suitable manner, a one-piece design also allows the assembly step that would otherwise be required to be dispensed with, thereby resulting in corresponding cost reductions.
Another aspect of the invention relates to a turbomachine, in particular thermal gas turbines, having a rotor, which comprises at least one blade with a shroud segment arranged on the radial end area of the blade, wherein the shroud segment has a stiffening structure that is raised relative to a shroud segment surface. In this case, a weight reduction of the at least one blade is achieved with a simultaneously good reduction in stress in that the shroud segment and/or the blade are designed according to one of the preceding exemplary embodiments. As a result, the weight of the rotor or the entire turbomachine is correspondingly optimized with a simultaneous improvement in its loading capacity, thereby making it possible to realize extended maintenance cycles. All shroud segments and/or blades of the rotor are preferably designed according to one of the preceding exemplary embodiments in order to achieve a maximum reduction in weight and stress. In addition, the masses being moved during operation of the turbomachine are correspondingly reduced, thereby producing additional advantages in particular with respect to fuel savings. Additional features of the invention are yielded from the claims, the exemplary embodiments as well as on the basis of the drawings. The features and combinations of features cited above in the description as well as the features and combinations of features cited subsequently in the exemplary embodiments are not just usable in the respective cited combination, but also in other combinations or alone without leaving the scope of the invention.